A high quality microphone such as the Gold line works better from the
standpoint of stray pickup if audio is coupled by a 1:1 microphone isolation
transformer, if the audio level right out of the Heil is adequate in level.
A step up transformer for the audio would be used if both isolation and gain
is needed and impedance matching.
Most ham transceiver inputs however, are low impedance compared to the older
models, and thus you need to look at the spec sheet for both mike and rig
mike input circuit to know which to do.
Sounds like the case of the Heil commons a power ground and the audio shield
ground, which it might if it has a Fet element. The case then, is picking
up some computer artifacts or switching. You might do a further test of
where it is originating, by turning off THE MONITOR. Many of those are high
RFI sources right from the CRT!
73,
Stuart K5KVH
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